You are right with your last sentence, but reddit is anything but niche. It attracts even politicians and other celebrities, albeit typically only for Q&As. Arnold Schwarzenegger and William Shattner post there for fun with their real names, who knows how many post under pseudonyms. The beauty of reddit is that it attracts even non-technical people who share their insight in their domain (usually anonymous, so to be taken with a grain of salt - but it's usually plausible precisely because reddit is so popular).
Reddit has grown significantly the last few years, but it still has only about 50-60 million daily users, compared to Facebook's nearly 2 billion daily users.
Don't get me wrong, I like Reddit. Before it I used Usenet, which died and after Usenet I was active on forums (most of those also seem to be gone now). I really prefer those topic based social media to the other user-based social media. But I've seen enough of them die before.
